1. Field of the Disclosure
The present disclosure relates to electronic circuit modules, and more particularly, to an electronic circuit module to which a metal cover is attached and a cover-fixing method for an electronic circuit module.
2. Description of the Related Art
A known electronic circuit module includes a circuit board on which a plurality of electronic components are mounted and a metal cover attached to the circuit board so as to cover the electronic components. Japanese Unexamined Patent Application Publication No. 2014-033025 discloses such an electronic circuit module. FIGS. 13 and 14A illustrates an electronic circuit module 900 disclosed in Japanese Unexamined Patent Application Publication No. 2014-033025.
As illustrated in FIG. 13, the electronic circuit module 900 includes a circuit board 920 on which electronic components 910 are mounted and a metal cover 930 that covers the circuit board 920. The metal cover 930 includes a top plate 931 that opposes the circuit board 920, a plurality of side plates 932, and a plurality of attachment legs 933. The circuit board 920 includes a plurality of lands 921 to which the attachment legs 933 are joined. As illustrated in FIG. 14A, each attachment leg 933 includes a bent portion 933a located at the outer periphery of the top plate 931 of the metal cover 930, an attachment-leg bent portion 933b, an attachment-leg fixing portion 933c that is in contact with the corresponding land 921 on the circuit board 920, and an attachment-leg insertion portion 933d. When the electronic circuit module 900 is viewed from above the circuit board 920, the bent portion 933a is located inside the attachment-leg fixing portion 933c, and the width of the bent portion 933a is greater than the width of the attachment-leg fixing portion 933c. 
The above-described structure has an effect of preventing the metal cover 930 from being deformed when the thickness of the metal cover 930 is reduced.
However, since the metal cover 930 of the electronic circuit module 900 is formed into a predetermined shape by a punching process, the base portion of the attachment-leg insertion portion 933d illustrated in FIG. 14A is not perfectly perpendicular. Therefore, there is a possibility that rising of the metal cover 930 will occur when the attachment leg 933 is inserted in an insertion hole. To prevent this, arc-shaped clearance portions 933e shown by the dashed lines in FIG. 14B may be formed in the base portion of the attachment-leg insertion portion 933d. However, when the arc-shaped clearance portions 933e are formed, gaps are formed between the arc-shaped clearance portions 933e and the land 921. Therefore, there is a risk that pin holes will be formed at the gaps during the joining process using a joining material, such as solder, and it is difficult to obtain a predetermined joining strength.